Image sensing devices commonly utilize Charged-Coupled Devices (CCD) or Complementary-Metal-Oxide-Semiconductor (CMOS) image sensors to capture image data of an imaged scene. CCD and CMOS devices include an array of photosensing devices, or pixels, that are exposed to light irradiated from the scene for a particular amount of time. This exposure time allows the individual pixels to “charge” or “integrate” until the pixels have a particular signal voltage value (also known as the pixel grey value.) These individual signal voltage values then may be correlated into digital image data representing the imaged scene.
Image quality is very important, and can vary based on a plurality of variables. For example, increasing the number of pixels within the array provides more image data, thus higher quality. Additionally, it is desirable to eliminate as much noise in the image data as possible. One known way to reduce noise (for example Fixed Pattern Noise) is correlated double sampling (CDS), particularly in CMOS imaging sensors. Correlated double sampling may be done in analog or digital domain.
CDS reduces the noise in the signal by calculating the difference between the signal voltage value (grey value), and a reset signal for the given pixel. Implementing CDS reduces the fixed pattern noise and other temporal noise from the image data.